This invention relates to an ultrasound diagnostic apparatus which generates an ultrasonic image on the basis of phase information and amplitude information contained in the reception signal obtained by scanning a subject by ultrasound, and more particularly to an ultrasound diagnostic apparatus which generates a stereoscopic image from ultrasonic images at high speed and displays the image.
Ultrasound has been applied to various medical instruments. A typical application of ultrasound to medical instruments is an ultrasound diagnostic apparatus for creating a tomographic image of soft part tissue of an organism using ultrasonic pulse reflection techniques. The ultrasound diagnostic apparatus displays a tomographic image of tissue without stress. As compared with the X-ray diagnostic apparatus, X-ray computed tomography apparatus (CT), a magnetic resonance imaging apparatus (MRI), or a nuclear medicine diagnostic apparatus, the ultrasound diagnostic apparatus has the advantages of enabling real-time display, being compact and inexpensive, being sufficiently safe without exposure to X rays, and enabling the imaging of bloodstream by the Doppler ultrasonography.
Because of those advantages, the ultrasound diagnostic apparatus has been widely used in diagnosing internal organs, such as a heart, the abdomen, the mammary gland, or the urinary organs, in internal medicine or in observing a fetus in obstetrics and gynecology.
Specifically, with the ultrasound diagnostic apparatus, simply applying an ultrasonic probe to the surface of a body enables the pulsation of a heart or the movement of a fetus to be displayed in real time. Because the apparatus is very safe, examination can be carried out repeatedly. Moreover, it is easy to move the apparatus to the bedside and carry out examination.
Furthermore, the ultrasound diagnostic apparatus is also capable of displaying the speed distribution of the bloodstream moving toward (or away from) the vibrators in the Doppler ultrasonography or the distribution of power values of the blood echo signal in the power Doppler method. The power Doppler method enables the perfusion of the vascular system to be sensed with higher sensitivity and is finding its way into the diagnosis of an abnormal bloodstream at the peripheral nerve level of a kidney or cancer of the liver.
Like in the fields of CT and MRI, in the field of ultrasonic diagnosis, there has been an increasing demand for three-dimensional images. For example, in the B mode imaging or color Doppler imaging, three-dimensional stereoscopic images have been displayed for the purpose of making a differential diagnosis or functional diagnosis of the shape of an internal organ or the passage of a blood vessel. Since a three-dimensional stereoscopic image has not only information on a two-dimensional image (or a tomographic image) but also information on the direction of its depth, it is expected that the shape of a tissue or the passage of a blood vessel will be known clearly.
Constructing an image having three-dimensional information requires an enormous amount of calculations, which leads to the problem of taking as long a time as several tens of seconds to several minutes to reconstruct and display a single image.
In the case of CT and MRI, because the nature of their diagnosis, spending a substantially long time in constructing a three-dimensional image may often be a negligible problem. In the case of ultrasonic diagnosis, since observation is made in real time, three-dimensional representation is hardly used in normal diagnosis. When a three-dimensional image is constructed in ultrasonic diagnosis, the image has to be reconstructed for observation after the data has been taken in (e.g., after examination), as with CT and MRI.
Although an image containing three-dimensional information enables an image viewed from any viewpoint to be reconstructed, observation from more than one viewpoint takes that much more time. It will be all right if a three-dimensional image (a still image) is observed from more than one viewpoint. In the case of images obtained one after another in real time as ultrasound diagnostic images, it is not always useful to reconstruct those images and see them from another viewpoint. Conversely, this action may make the procedure more complicated and troublesome.
Moreover, accurate three-dimensional information may not be necessary. For example, only an image with a depth effect may be needed to get more accurate information on the shape of a tissue or the passage of a blood vessel.